A magnetic linear drive for accelerating a projectile U.S. Pat. No. 4,817,494.
U.S. Pat. No. 5,719,451 also describes a magnetic linear drive where it is used, for example, in pumps for liquids. The linear drives described therein have the common feature that a magnet coil accelerates an armature in the axial direction of the coil.
Further, GB 10 68 61 0 describes a magnetic linear drive. The drive described therein is a drive for a valve in which a channel for liquid is shut off or opened by the movement of an armature.
There, the armature has a permanent magnet whose magnetic flux in its interior is directed in the movement direction of the armature, and at right angles to the axial direction.
At each of its limit positions, the armature runs into mechanical stops such that one pole of the permanent magnet always comes into contact with the stop, and such that the magnetic effect of the permanent magnet holds it against the stop.
If a current is passed through the coil, then the magnetic effect of the current first of all has to cross the holding force of the permanent magnet against the stop. This results in a delay to the armature acceleration. Furthermore, during its movement toward a limit position, the armature is drawn toward the stop only immediately before reaching it, since the airgap located between the pole of the permanent magnet and the stop surface becomes sufficiently reduced in size only toward the end of the movement.